This application claims priority from Korean Patent Application No. 2002-46794, filed on Aug. 8, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a microfluidic device for use in a biochip, and more particularly, to a microfluidic device that controls fluid flow by using the combination of a natural capillary force and an externally applied pressure generated by pumping.
2. Description of the Related Art
Microfluidic devices known as the most crucial element of biochips can be implemented based on various kinetics principles. For example, a microactuating method using a micro pump and a micro valve, which are connected to a micro channel or chamber, an electrophoretic method of inducing fluid flow by applying a voltage across a micro channel, a capillary flow method using capillary force, and other methods can be applied to accomplish microfluidic devices.
Various kinds of microfluidic devices manufactured based on such operating principles include active microfluidic components, such as micro pumps and micro valves, that directly control fluid flow, flow stoppage, or flow rate, and passive microfluidic components, such as channels or chambers, that affect fluid flow, flow stoppage, or flow rate through their topology or shape changes. These microfluidic devices have a wide range of applications, for example, in protein chips, DNA chips, drug delivery systems, and micro biological/chemical reactors, which require precise and accurate flow controls.
Among various microfluidic devices, ones using capillary flow control fluid flow, flow stoppage, and flow rate using an attractive force or repulsive force generated spontaneously due to the surface tension exerted between the inner surface of a micro tube and fluid. Most capillary microfluidic devices do not include an active driver, so they do not require an additional power supply and hardly cause problems. However, high performance biochips cannot be implemented exclusively using capillary flow in some applications. For example, a biochip using an electrochemical detection method requires the washing away of floating, unbound small particles or colloids, or reaction products loosely bound to a sensing electrode after biochemical reactions of a sample on the sensing electrode and buffer exchange for electrochemical detection. This buffer exchange process requires forced fluid flow by an external force.
Typical examples of capillary microfluidic devices are disclosed in U.S. Pat. Nos. 6,271,040 and 6,113,855. U.S. Pat. No. 6,271,040 suggests a diagnostic biochip having a structure where a fluid sample is delivered by only capillary force for a reaction in a chamber and a channel, and an optical method is applied to detect the reaction of the sample and reagents. U.S. Pat. No. 6,113,855 suggests capillarity-inducing hexagonal structures appropriately arranged in a chamber to induce capillary force.
Most capillarity-based biochips known thus far are limited to optical detection and do not require a microfluidic control device having a buffer exchange structure. The above-described U.S. patents also teach only devices and methods for controlling fluid flow or flow stoppage by changing a channel structure. However, in biochips using electrochemical detection, which require buffer exchange as described above, there is a need to forcedly control fluid flow by applying an external force in order to fully wash away unnecessary substances and to exchange buffer solutions in a chamber, which cannot be achieved through common capillary flow.